DE2724763C2 - Process for cleaning and decomposing a gas mixture - Google Patents

Description

The invention concerns! a process for cleaning and disassembling one of several, different high boiling points Components of existing gas mixture in which the gas mixture is connected in series Cleaning and adsorption beds are conducted, in which the adsorption at higher levels and the desorption take place at lower pressure in the pressure change, with water vapor and possibly CO in the cleaning bed. and other higher-boiling components of the gas mixture are retained while in the adsorption bed one or more lower boiling components are preferentially adsorbed, so that one of impurities free fraction is obtained which is enriched in the one or more weakly adsorbable components is.

For some years now, pressure swing processes have been used in the technology of adsorptive gas separation and these have proven to be practicable for many purposes. In these processes, the adsorption takes place under a higher pressure than the desorption of the previously adsorbed components, which is brought about simply by lowering the pressure, if appropriate down to subatmospheric pressure and, if appropriate, by additionally passing a flushing gas over it. The pressure change takes place with In a paying only after minutes or seconds! Measure of time. Another essential feature of the known pressure swing process is that neither heating during desorption nor cooling during adsorption is carried out. Since these processes thus run essentially at a constant temperature, preferably at room temperature, they are extremely favorable in terms of energy. In the known pressure swing process, a loading front of the preferably adsorbed components is generated within the adsorbent mass, which migrates towards the outlet of the adsorber during the adsorption process and is shifted in the opposite direction during desorption, so that the loading front back and forth during the two processes oscillated.

A known method of this type is described in DE-OS 20 55 425.
If zeolites are used to break down a gas mixture, then it must be ensured that the gas mixture to be broken down is pre-dried, ie pre-cleaned, enters the adsorber, since zeolites, due to their lattice structure, preferentially adsorb water over all other substances, which is when undried gases are used The consequence would be that the adsorption capacity of the zeolites with respect to the other components would be blocked entirely or at least to a considerable extent. In the known method, which relates to the generation of a fraction that is enriched with oxygen compared to air, the actual adsorbent dryers are therefore connected upstream, which are either filled with silica gel or with Zeollth.

Since a pair of dryer-adsorbers that belong together is always connected by a pipe, the restoration the adsorption pressure in both containers in the known method is a particular problem is. In the known method, a throttle point is therefore set up between the two containers, which it allowed to increase the pressure in the actual adsorber during the repressing with raw gas from The input end of the dryer is made to slow down.

However, the known method has significant disadvantages. First, it is always necessary to carry it out two separate containers for the desiccant and for the adsorbent and connected by a line secondly, the gas required for repressing the adsorber must be passed through the dryer. This will make the water loading front in the dryer In Shifted towards its outlet end, which can have the consequence that the water loading front After a long period of operation, sew it to the outlet end of the dryer and water will break into the adsorber or that the dryer must be considerably oversized for safety reasons.

A pressure build-up with a dry and CO ₂ -free gas, as is e.g. B. occurs in the known method from the direct current relaxation of an adsorber, can only be carried out via the outlet end of the adsorber, which leads to contamination of the outlet layer. When such a gas is introduced through the dryer, there is a risk that water from the dryer will be desorbed by this gas and into the zeolite

layer is worn. So if you want a higher product To produce purity with the known method, the use of this gas must be dispensed with which leads to a considerably poorer product yield.

It is the object of the present invention to eliminate these disadvantages and to create a method of the type mentioned at the beginning which allows _{gases contaminated with water, CO 2} or other higher-boiling components to be broken down more economically and reliably than before.

According to the invention, this object is achieved in that the structure of the necessary after the desorption Adsorption pressure of at least 20 *> by pressing in a gas consisting of the lower-boiling component or components between the cleaning and Adsorption bed takes place.

In the method of the invention, the pressure build-up will therefore be not accomplished by introducing a gas over the cleaning bed as in the known method, but by introducing it at a point located between the cleaning bed and the adsorption bed.

A process is known from DE-PS 17 69135 in which a gas is blown in between two molecular sieve beds located in a container, but the process of this patent is a completely different process than that of the present invention. First of all, the known process is not a pressure change process, but a temperature change process, so that the problems inherent in the pressure change process do not play a role in the known process Adsorption of CO ₂ is used to be able to regenerate separately from the smaller one, which acts as a dryer. For this purpose, a seldom tap is provided between the two Schüttur.gen and the regenerator gas is either fed in or out through this seldom tap, which is the case with the known method In principle, there is no difference, but care is taken that the circulating regenerator gas only flows through the dryer at the very end.

The method according to the invention has the advantage that any residual H ₂ O, CO2 or possibly other impurities present on the cleaning bed is forced towards the inlet end of the cleaning bed by the pressure build-up, so that "><> switches on after switching to adsorption The process according to the invention offers a particular advantage when more than one adsorber is used, since the pressure relief gas flowing out from the outlet end of one adsorber can be used to at least partially build up the pressure of another adsorber achieve a significantly higher product yield than with the known process.As this expansion gas is introduced into the adsorption bed via its inlet end, a water- and CO ₂ -free gas can also be used which already contains the preferably adsorbed components without it a worsening The purity of the product comes into play. It is thereby z. B. not necessary to keep free adsorption capacity in the adsorption bed for the relaxation cycle in order to prevent the adsorption front from breaking through.

The method according to the invention can be applied to all gas mixtures which on the one hand contain water and CO2 are and possibly also contain high-boiling impurities and, on the other hand, of several Components exist, at least one of which is in pure form, or at least in worldly pure form should be won.

With the aid of the method according to the invention, pure sour spoons or oxygen can be obtained from air, for example Obtain enriched air, which In the chemical industry, in the iron and steel industry, in combustion processes or can be used in wastewater treatment. Likewise, the inventive Also use processes to obtain or enrich hydrogen from a steam reforming gas. But also for the decomposition of hydrocarbon mixtures, which are gaseous at normal temperature are, the inventive method can be used with success.

The cleaning compound and the adsorbent are advantageous for carrying out the method according to the invention housed in a single adsorber. So it is a construction that is significant is simpler and cheaper than the two separate adsorbers that the initially discussed process of the prior Technology requires.

The Druckaulbau according to the invention, which by pressing of a gas takes place between the two beds, is preferably carried out with one in the course of the dismantling process won fraction. Using a faction has the advantage of that a gas is used which is free from the components deposited in the cleaning bed of the raw gas, so that a possible residual load in the cleaning bed is pushed back in the direction of takes place at the inlet end without contamination of the adsorption bed occurring at the same time. As one such a fraction can be viewed, for example, as the clean gas or that after the adsorption step has been completed Gas remaining in the cavities of an adsorber, which is due to pressure equalization is introduced into this with the adsorber to be repressed. When using this pressure release gas a fraction is used that would otherwise be released as residual gas.

Since, however, after a fraction has been introduced between the two beds until the pressure builds up to at least 20% of the adsorption pressure, the pressure build-up is sufficient to prevent the adsorption front from tearing through during further pressure build-up, the invention provides for the last pressure increase up to the adsorption pressure To accomplish raw gas, which, however, is blown into the adsorber from the inlet end of the cleaning bed in order to keep the adsorber bed free of H ₂ O, CO ₂ and possibly also other impurities and not to reduce its capacity unnecessarily. However, since the first substantial increase in pressure has already taken place, when using the raw gas to build up pressure in this process variant there is no risk of impurities breaking through to the adsorption bed, which in any case would be undesirable.

According to a further development of the inventive concept, it is provided in the method according to the invention, if necessary, two adsorbers of one adsorber battery bypassing the cleaning bed of the second Connect the adsorbers one behind the other, so that in this process variant the raw gas is successively

giingsbett, a first and a second adsorption bed flows through.

This process variant has the advantage that the capacity of the first adsorption bed is fully utilized in that there is the possibility of pushing the loading front into the second adsorption bed without that some contamination of the clean gas to be recovered occurs. This way becomes the first Adsorption bed loaded until its capacity is completely exhausted and the second only insignificantly preloaded, so that the overall process is very favorable.

The cleaning and adsorption beds according to the invention can be combined with any known adsorbent be equipped. All you have to do is achieve the intended purpose. So did for the cleaning beds Silica gel, activated carbon, alumina gel and zeolites and for the adsorption beds zeolites and activated carbon proven, whereby the type of zeolite to be selected depends on the type of separation task set for it depends.

The duration of a switching cycle can be different in the method according to the invention. In general the duration is 10 to 20 minutes. However, it can be shortened to, for example, 5 minutes and in Extreme cases only last a few seconds.

The invention is further described with reference to a system with three adsorbents shown schematically.

However, the invention is not limited to such systems limited with three adsorbers, but can also be applied equally to those with more adsorbers, if, for example, it should be planned to increase and decrease pressure in several individual steps complete what usually requires the connection of further adsorbers.

The system shown in Fig. 1 consists of three adsorbers I. 2 and 3 with the cleaning beds 10, 20 and 30 and the adsorption beds 11, 21 and 31. In a compressor 4, the raw gas is compressed to the pressure required for adsorption and through a line 5 and a valve 12 are fed to the cleaning bed 10 of the adsorber 1, where H ₂ O, CO; and if necessary other components are exempted. The gas pre-cleaned in this way then immediately enters the adsorption bed II of the adsorber I, where one or more components of the raw gas are preferentially adsorbed. The clean gas freed from these components flows through a valve 13 and a clean gas line 6.

If the adsorption front of the preferably adsorbed components has the end of the adsorption bed 11 of the Adsorbers 1 reached, then the valves 12 and 13 are closed and the raw gas by opening valves 22 and 23 passed through the cleaning bed 20 and the adsorber bed 21 of the adsorber 2, where the same Process repeated. At the same time, a valve 14 is opened, and that which flows out of the adsorber 1 Pressurized gas occurs after opening a valve 36 between adsorption bed 31 and cleaning bed 30, which are are at the lowest process pressure at this point in time in order to increase the pressure there again. After pressure equalization has taken place, the valves 14 and 36 are closed again.

The desorption of the components adsorbed in the cleaning bed 10 and in the adsorption bed 11 of the adsorber I now takes place. For this purpose, a valve 15 is opened and the pressure in adsorber 1 is further reduced. Residual gas flows off through a line 7. The lowering of the pressure is interrupted at the lowest process pressure by closing the valve 15, this lowest process pressure possibly being atmospheric pressure or, if necessary, also a lower pressure which can be achieved with the aid of a vacuum pump connected to line i and not shown in the figure can. If it is preferable not to work under negative pressure, it can be advantageous, with the valve 15 still open, to introduce some pure gas into the adsorber 1 from its outlet end by opening valves 14 and 24 to support the desorption.

Now the pressure in the adsorber 1 must be built up again. This is done by introducing expansion gas from the adsorber 2, whose adsorption phase has just ended, via the valves 24 and 16. Since this pressure _{build-up takes place with dry, CO 2} -free gas for the cleaning bed 10 in countercurrent to the adsorber, a there is after the Desorption Residual load pushed back in the direction of the inlet end of the cleaning bed, ie the effect of the previous desorption is thereby increased, which in the end leads to a downsizing of the dryer.

The further pressure build-up up to the adsorption pressure takes place after closing the valves 24 and 16 by opening the valve 12 by introducing moist raw gas in the cleaning bed 10 and the adsorption bed II of the Adsorbers 1. After the pressure build-up has been completed, the valve 13 is opened, and the TakU just described sequence begins again.

To carry out the second variant of the method, as soon as the adsorption front of the adsorbed " Components reached the end of adsorber I, valve 13 closed and valves 14 and 26 opened-J5 net, so that when the valve 23 is open, clean gas then flows out through line 6 again. The adsorption cycle is ended when the mass transfer zone has fully passed into the adsorption bed 21 of the adsorber 2 is.

FIG. 2 shows a timing diagram for the system shown in FIG. I, which consists of three adsorbers reproduced.

The top bar shows the process steps in adsorber 1, the middle one in adsorber 2 and the bottom one in adsorber 3. In the scheme, "E" means the expansion, which takes place with simultaneous pressure equalization with another adsorber. The two pressure build-up stages are designated by "DR" and "DR1" - firstly by means of expansion gas from another adsorber and secondly with the help of raw gas. "VB" means the section of the pre-loading when, according to the second process variant of the invention, two adsorption beds are connected one behind the other until the mass transfer zone has fully entered the second adsorption bed. If this process step is omitted, the time available for the pressure build-up DR 2 is extended by the corresponding amount.

The invention is further based on a few numerical examples made clear.

example 1

This example shows the extraction of an 02-rich Fraction from air, with the gas to be separated only flowing through an adsorption bed.

Three adsorbers, each with a cleaning bed and an adsorption bed, were used in the process.

Each cleaning bed was filled with 150 kg of world-pore Sillkagel or 150 kg of activated alumina and activated carbon, each adsorption bed with 2750 kg of zeolite molecular sieve Type 5A charged.

Adsorption time:

Cycle time:

Feed gas:

Adsorption pressure:
Adsorption temperature
Desorption pressure:
Product:

Product composition:

Product printing:

3 min
9 min

861 NmVh of air with a water content of 4.8 g / Nm ³ and a CO ₂ content of 330 vpm.

4 bar (abs.)
293 K

0.15 bar (abs.) ■ '

150 NmVh (dry and COj-free)
90 vol-96 O ₂

6 Vol-96 N ₂

4 vol-96 ares

3.7 bar (abs.).

Example 2

In this example, which also shows the recovery of an O ₂ -rich fraction from air, use was made of the second variant of the method according to the invention, ie the gas flowed through two adsorption beds one after the other.

In the process, three adsorbers, each with a cleaning and. an adsorption bed is used. Each cleaning bed was filled with 120 kg of wide-pore silica gel or 120 kg of activated alumina and activated carbon, each adsorption bed is charged with 2250 kg of zeolite molecular sieve type 5A.

Adsorption time:

Cycle time:

Feed gas:

Adsorption pressure:
Adsorption temperature:
Desorption pressure:
Product:

Product composition:

Product printing:

3 min
9 min

694 NmVh of air with a water content of 4.8 g / Nm ³ and a CO ₂ content of 330 vpm.

4 bar (abs.)
293 K

0.15 bar (abs.)

150 NmVh (dry and

CCV free)

90 vol-96 O ₂

6 VoI- *. N ₂

4 vol% Ar

3.7 bar (abs.).

Example 3

Three adsorbers, each with a cleaning bed and an adsorption bed, were used in the process. Each cleaning bed was filled with 250 kg of wide-pored Sillkagel or 250 kg activated alumina and activated carbon, each adsorption bed with 3500 kg zeollthic molecular sieve Type 5A charged.

10

20th

25th

30th

35 adsorption tent:

Cycle tent:

Feed gas:

Adsorption pressure:
Adsorption temperature:
Desorption pressure:
Product:

Product composition:

Product printing:

3 min
9 min

1320 NmVh air with a water content of 4.8 g / Nm ¹ and a COj content of 330 vpm.

4 bar (abs.)
293 K

0.15 bar (abs.)

150 NmVh (dry and

COi-free)

90 vol% O ₂

6 vol% N ₂

4 vol% Ar

3.7 bar (abs.).

Example 4

In this example, the production of hydrogen from a steam reformer gas with the aid of the invention Process demonstrated, with the gas to be separated only flowing through an adsorption bed became.

Three adsorbers, each with a cleaning and adsorption bed, were used in the process. Any cleaning bed was with 100 kg of activated alumina and kg of activated carbon, each adsorption bed with 2000 kg Zeolillian molecular sieve type 5A charged.

40

45

50

In this example air was in an adsorber system dismantled in the conventional manner, d. H. neither the pressure equalization according to the invention nor one took place Series connection of adsorbents Adsorption time:

Cycle time:

Raw gas:

Raw gas composition:

Adsorption pressure:

Adsorption temperature:

Desorption pressure:

Production

setting:

Product printing:

4 min
12 min
1000 NmVh
72 vol-96 H ₂

12 vol% CO

13 vol% CO ₂
3 vol% CH ₄

12 bar (abs.)

303 K

0.1 bar (abs.)

99 vol% H ₂

0.7 VoL-96 CH ⁴

0.3 vol% CO

CO ₂ less than 10 vpm.

H ₂ O less than 1 vpm.

11.5 bar (abs.).

For this purpose 2 sheets of drawings

Claims (4)

Patent claims: 1. A method for cleaning and breaking down a gas mixture consisting of several, different high-boiling components, in which the gas mixture is passed through cleaning and adsorption beds connected in series, in which the adsorption takes place at a higher pressure and the desorption at a lower pressure in a pressure change, whereby in the cleaning bed Water vapor and possibly CO ₂ and other higher-boiling components of the gas mixture are retained, while one or more lower-boiling components are preferentially adsorbed in the adsorption bed, so that a fraction free of impurities is obtained which is enriched in the component or components that are weakest to adsorb, characterized in that the necessary build-up of the adsorption pressure after desorption takes place by at least 20% by pressing a gas consisting of the lower-boiling component or components between the cleaning bed and the adsorption bed. 2. The method according to claim 1, characterized in that when using one of several cyclically switchable cleaning and adsorption beds existing Adsorberbatterle the pressure build-up by pressing in a pressure relief valve flowing from the inlet or outlet end of another adsorption bed and / or product gas takes place. 3. The method according to the preceding claims, characterized in that in a partial Build-up of the adsorption pressure by forcing a gas between the cleaning and adsorption bed the further pressure build-up by pressing in the gas mixture to be cleaned and broken down takes place from the entry side of the cleaning bed. 4. The method according to the preceding claims, characterized in that the outlet end an adsorbent flowing off on the weakest adsorbable component enriched fraction for further enrichment between a cleaning and an adsorption bed introduced and the fraction free of impurities from the outlet end of the latter adsorption bed is removed.